This application claims priority to Japanese patent application No. JPAP11-188536 filed on Jul. 2, 1999, the entire contents of which are hereby incorporated by reference.
1. Field
The present invention relates to an optical disk recording and reading apparatus, and more particularly to a lens actuator for optically recording and reading data on a disk.
2. Description of the Related Arts
A lens actuator for use in an optical disk recording and reading apparatus is required to employ a movable supporting member capable of reducing as much lost motion as possible, caused by a non-lineality factor of a lens actuator motion. For this reason, a set of linear-shaped springs for supporting the movable supporting member has been employed in a lens actuator needed to be controlled with a high degree of precision. Japanese Laid-Open Patent Publication No. 09-190636 (1997) is one example, describing a structure of an object lens holder. In this structure, the holder is configured to surround a driving coil generating a thrust for moving the holder in focus and tracking directions.
An optical disk recording and reading apparatus employing the above-mentioned lens actuator needs to be low profiled especially when it is used in a note-book type personal computer, for example. This is, of course, because the note-book type personal computer requires thinner components than desktop type personal computers do due to portability requirements of the note-book type personal computer. On the other hand, since a high speed trackability becomes more important for a lens actuator with increases of recording density and of an operating speed of a system, the lens actuator needs to be improved in a frequency response particularly during the time when an object lens is moved for the focusing and tracking operations. In particular, the driving coil is needed to improved to have a high sensitivity, and a high natural oscillation frequency in a rigid mode and a high natural oscillation frequency of a movable supporting structure in an elastic deformation mode.
In order to meet the above-mentioned requirements, an optimum designing is needed under consideration of reductions in size and weight and provision of greater rigidity. More specifically, the lens holder is needed to be designed to have an optimum shape. Also, for such a lens holder, it is worth to consider use of a sophisticated plastic resin having a high rigidity ratio, a high ratio of an elastic coefficient to a mass density. Further, it becomes more important to consider a measure for improving reliability of heatsink relative to a self-produced heat depending upon a power consumed by the driving coil. This is due to a necessity of high speed trackability compatible to various types of recording and reading medium sold in the market.
However, in the structure described in the above reference, the driving coil produces an inferior heatsink effect since the holder surrounds the driving coil for the purpose of improving rigidity. In general, making a component compact and lighter will lead a deterioration of heatsink and allow a smaller amount of current flow due to the heat problem. Therefore, in this case, either one of a high speed and a reliability is normally sacrificed.
On the other hand, an effect from a resonance produced in a rigid mode can be reduced by a method of matching a center of measurement which is a principal point of a lens as and three centers in a movable supporting structure which are a thrust center, an inertia center, and an elastic (supporting) center. This method is known by a principle of Abbe and a principle of alignment. According to it, various kinds of movable supporting structure have been developed for the lens actuator. However, dimensions around the lens is extremely severe and the position of the lens needs to be arranged in an offset position because of the requirements for thinning the structure of the optical disk recording and reading apparatus. With this structure arranging an offset position, it is difficult to eliminate the inertial linear moment and to match the inertial center to other centers of thrust, elastic, and so on. To measure this problem, a metal material having a relatively high mass density is used as a mass adjusting member. However, such a metal material increases manufacturing cost and the weight of apparatus, which reverses the above-mentioned recent requirements.
The present invention provides a novel lens actuator for use in an optical disk recording and reading apparatus. In one example, a novel lens actuator includes a moving member and a mass balancing member. The moving member includes a holder for holding an object lens movably in tracking and focus directions, a driving coil for generating a thrust for driving the holder in the tracking and focus directions, and a set of supporting members for supporting the holder and supplying power to the driving coil. The mass balancing member is positioned diagonal to the object lens held on the moving member by the holder and is configured to make contact with the driving coil within the moving member.
The mass balancing member may be made of metal.
The mass balancing member may have a portion protruding from the holder. In this case, the portion is arranged in a space formed in a base of the lens actuator without contacting the base, wherein the space is filled with a viscoelastic dumber material.
The holder may be configured to allow portions of the driving coil to be out of the holder and exposed to air, wherein the portion of the driving coil includes a magnet-effective portion and coil surfaces excluding a surface at which the driving coil is mounted on the mass balancing member.
The set of supporting members may be made of lineally-elastic material which elastically deforms in accordance with a thrust generated by the driving coil.
The present invention further provides an optical disk recording and reading apparatus which includes one of the above-mentioned lens actuator, wherein the object lens is to gather laser light on an optical disk.